Identification of the Chemical Forms of Heavy Metals in Municipal Sewage Sludge as a Critical Element of Ecological Risk Assessment in Terms of Its Agricultural or Natural Use

Abstract

The present study aimed to demonstrate that identification of the chemical forms of heavy metals in sewage sludge produced in municipal Wastewater Treatment Plants (WWTPs) is a critical element of ecological risk assessment, especially in terms of its agricultural or natural use. The concentrations of seven heavy metals (Cd, Cr, Cu, Ni, Pb, Zn and Hg) were determined using inductively coupled plasma optical spectrometry (ICP-OES) and cold vapor atomic absorption spectrometry (CV-AAS). The chemical forms of heavy metals were analyzed in accordance with the sequential extraction method proposed by the Community Bureau of Reference (BCR). Sludge samples were collected at the five municipal WWTPs located in the largest industrial area in the country, i.e., the Upper Silesian Industrial Region (southern Poland, central Europe). The ecological risk was assessed by calculating the Potential Ecological Risk Factor (ER), Risk Index (RI), Risk Assessment Code (RAC), Individual Contamination Factor (ICF), Global Risk Index (GRI) as well as the author’s indices, i.e., Individual Ecological Risk (IER) and Global Ecological Risk (GER). To demonstrate the differences between the level of ecological risk posed by the different heavy metals, sludge samples were collected at two specific points of the processing line. Considering the chemical forms of heavy metals, the highest ecological risk was posed by Zn, Cd and Ni, while in the case of their total concentrations, by Cd and Hg. The obtained results confirm that quantitative determination of the total content of heavy metals in sewage sludge is not a sufficient criterion in assessment of the ecological risk that these elements pose to the natural environment and living organisms. Moreover, multivariate statistical analysis revealed a significant correlation between the concentrations of heavy metals, which indicates that they plausibly originate from the same source of pollution.

Comparison of the Potential Ecological and Human Health Risks of Heavy Metals from Sewage Sludge and Livestock Manure for Agricultural Use

“…In order to prevent the adverse effects of the agricultural use of sewage sludge and livestock manure induced by heavy metals, potential ecological and human health risks must be assessed [ 23 , 24 ]. The assessment of the potential ecological risks of heavy metals commonly uses the geo-accumulation index, single-factor pollution index, Nemerow’s synthetic pollution index, and ecological risk index [ 25 , 26 , 27 , 28 ].…”

Stabilization of Municipal Solid Waste Fly Ash, Obtained by Co-Combustion with Sewage Sludge, Mixed with Bottom Ash Derived by the Same Plant

“…Comparing the leaching data of different combustion lines, it is very interesting to notice that in FA, the concentration of leachable Zn is substantially irrespective of the amount of co-incinerated SS. On the contrary, the amount of soluble Pb increases with the amount of SS, probably due to the presence of this metal in sewage sludge [26]. Concerning P, an element that is well-known to be abundant in SS [27], its concentration appears to decrease in FA with the increase of co-incinerated SS.…”

Comprehensive Evaluation of Metal Pollution in Urban Soils of a Post-Industrial City—A Case of Łódź, Poland

“…Weak relationship was detected for Cd (0.31). As pointed out by [ 7 , 13 , 14 , 15 ], total metal contents are not sufficient to assess their potential toxicity. Therefore, further considerations are based on mobile fractions only.…”

“…The behavior of potentially toxic elements in the environment, their bioavailability, and toxicity are more related to the forms in which they occur in the soil than to their total content. However, the total metal content is usually taken as the criterion for soil contamination assessment, regardless of their actual availability [ 7 , 13 , 14 ]. In making decisions aimed at reducing soil pollution and the improvement of soil functions, it is critical to analyze the content of mobile metal fractions in soil [ 15 ].…”

“…The analysis of metal content in urban soils is the subject of numerous publications [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Particular attention is paid to green areas due to their use for recreation and the possibility of people’s exposure to contact with contaminated soil [ 2 , 9 , 21 , 22 , 23 ].…”